Hi wondering if anyone can help, have 99 plate a3 1.9 tdi 177k, recently had an overheating problem where needle was goin as far as poss, had a second thermostat fitted and new temperature sender, I drive maybe 5 miles now the needle moves from 90 to 100 and sits for a few minutes then goes back to 90, do another 5 miles the same thing happens again then it's fine for a while, usually drive 15-20 miles when I stop bottom rad hose is still cold with the heater also blowing hot and cold occasionally, any help would be appreciated, thanks in advance